clang-tidy - readability-const-return-type

Checks for functions with a const-qualified return type and recommends
removal of the const keyword. Such use of const is usually superfluous,
and can prevent valuable compiler optimizations. Does not (yet) fix trailing
return types.

Examples:

constintfoo();constClazzfoo();Clazz*constfoo();

Note that this applies strictly to top-level qualification, which excludes
pointers or references to const values. For example, these are fine: